The present invention relates generally to a monochromator-testing system and method, and, more particularly, to a monochromator-testing system and method for use in an automated chemistry-analyzing system for analyzing blood or other body fluids.
The chemical analysis of blood or other body fluids or serums is a vital part of medical diagnosis. Testing for various serum constituents, such as glucose or heart enzymes, for example, or for some other medically significant factor, can be performed in a manual or automated process by adding specific amounts of various reactive chemicals or reagents to a sample of the serum in a specific sequence and under specified conditions of temperature and time. The light-transmittance value of the resulting test chemistry is then measured, and this value can be used to determine the amount of the particular constituent being measured in the serum. The term "serum" is used to designate any biological fluid.
More specifically, in analyzing a serum specimen, a sample of the specimen is typically placed in a test tube or other appropriate container; and one or more specific reagents are added, depending upon the particular test to be performed. When the required chemical reactions have taken place, a sample of the completed test chemistry is removed from the test tube; and the light-transmittance value of the test chemistry is ascertained by using a spectrophotometer or the like. This value can be used to calculate the optical density of the chemistry; and from this, the concentration of the constituent of interest in the serum can be ascertained. Automatic systems for performing such analyses are disclosed, for example, in U.S. Pat. No. 3,901,656 and No. Re. 28,803.
Determination of the concentration in a serum specimen of constituents of interest requires determination of the optical densities of the serum solutions and the test chemistries. This determination is made by passing light of a selected wavelength or wavelengths through samples of the serum solutions and test chemistries to measure their light-absorbance values at the selected wavelength or wavelengths. The terms "optical density" and "light absorbance" are used synonymously to describe the effect of the test solution on light that passes through it. Light transmittance may also be used to describe serum solution testing. Correct results require accurate determinations of the light-absorbance values of the serum solutions and test chemistries. A variety of factors can interfere with the accuracy of these determinations. For example, the presence of bubbles in the test solution can cause measurement errors. Similarly, factors, such as turbidity or settling, can also interfere with the accuracy of the measurements.
Moreover, a number of constituents normally present in varying amounts in the serum itself may introduce significant errors into the measurements. These endogenous transferring substances include bilirubin, hemoglobin, lipids, and the like. Such substances absorb light at various specific wavelengths; and when the maximal absorbances of the interfering substances are at wavelengths close to those wavelengths at which the test chemistries are to be measured, the optical measurements will be severly affected unless corrected or compensated for in some way.
Techniques have been developed to reduce the effect of these interferences with the accuracy of the measurements. For example, where the effect of the interference on the optical density of a solution is known to be significant in one range of wavelengths and nominal in others, several measurements of the same test solution may be taken at different wavelengths. One or more wavelengths may be selected to provide a measure of the significant determination of an interfering factor without a significant contribution from the factor being measured by the test chemistry. Other wavelengths may be selected to provide a significant determination of the factor being measured by the test chemistry with relatively nominal interference. From such data, the contribution of the interference may be determined and compensated for in analyzing the test results.
Such techniques have generally been limited to manual laboratory procedures practiced by trained technicians, although some automatic serum chemistry-analyzing machines have the limited capability of practicing such techniques with a few selected wavelengths. In such systems, this has been accomplished by providing a plurality of filter elements and selectively inserting them into the light path. Such systems are limited to only a few light wavelengths and provide little flexibility.
Where the system is capable of generating data at only a few wavelengths within the milliseconds that represent substantially the same time for data comparison and use, the few data points, while providing a measure of the characteristics of a serum solution and test chemistry at the wavelengths of data points, provide no reliable information on the light-absorbance characteristics of serum solution and test chemistry between the data points. Isolated data points cannot be used to reliably establish whether the light absorbance is increasing or decreasing with varying wavelength adjacent the data points and, of course, can provide no information on the rate of change of any such variation. Three data points, for example, may appear to lie on a straight line that represents constant light absorbance as a function of wavelength when the light absorbance actually varies substantially and significantly between the data points. Determination and use of reliable information on such variations were not possible in automatic serum chemistry testing systems.
Such systems have also used an intense polychromatic ("white") light passing through the test solution. Such intense polychromatic light includes wavelengths that can effect changes in the serum constituents, the reagents, and the test chemistry.